Lead-acid storage batteries have long been an efficient and effective source of power for a variety of applications. From every indication it is clear that such batteries will continue in heavy use into the indefinite future. While much work has been done to develop nickel-cadmium batteries, nickel-iron batteries, lithium, sodium-sulphur systems and other electrochemical storage systems, and other alternative power sources, lead-acid batteries remain and are likely to remain the best choice for strong reasons, including their relatively low cost.
The economy and dependability of lead-acid storage batteries makes such batteries practical for a vast number of applications, including stand-by power systems for communication and emergency lighting, automotive and truck-starting applications, electric vehicles, wheel chairs, uninterruptable computer power supplies, and systems for solar and wind power storage, to name just a few.
Lead-acid storage batteries present many problems and have many shortcomings which, despite decades of efforts, have not been overcome. Among these are the potential for explosions, the problem of human contact with lead including during manufacture, and low energy density problems.
Conventionally made lead-acid storage batteries are susceptible to explosions. The seriousness of the problem of potential battery explosions is expressed in an article in the May 1993 issue of Battery Man magazine, entitled "Valve Regulated Lead Acid Recombinant Batteries SLA," by John James, Eugene I. Aidman, Galina Aidman and Joseph A. Orsino, two paragraphs of which are as follows:
"[L]ead-acid batteries . . . are by their very nature gas producing systems. The gases produced, unfortunately, are predominantly hydrogen and oxygen in a ratio conducive to violent explosions if inadvertently subjected to flames or sparks, which are two indigenous environmental conditions. PA1 "No effort should be spared in the attempt to
make the lead-acid battery a human and environmentally safe product. The many lawsuits in the courts today attest to the fact that, under unfortunate circumstances, the use of the lead-acid battery may injure people and produce untenable environmental damage."
Reliable government statistics indicate that there are over 6,000 injuries reported annually from battery explosions.
Conventional lead-acid storage batteries have intercell connections inside the battery just under the top wall. Such connections are typically made by welding an upstanding projection from a plate bridge of one cell to an upstanding projection from the plate bridge of the adjoining cell. The weld is through a hole in the battery container partition between cells. In a 12-volt post-style battery there are five such welds, while in side-terminal batteries there are seven. These welds are made above the top of the plates in the headspace of the battery where hydrogen and oxygen gases collect during the electro-chemical operation of the battery.
In addition to the intercell weldments, plate groups within each battery cell are welded to their respective plate bridge along the tops of the plates. Thus, there are a substantial number of welds within the battery.
Miswelds or broken welds at any of the weld locations are sources of electrical arcing within the headspace of the battery. Such internal arcing ignites the hydrogen-oxygen gas mixture in the headspace, causing accidental explosions.
The long-standing problem of battery explosions has remained unsolved.
It is well known that human exposure to lead should be minimized. Therefore, when use of lead is necessary or beneficial, it is well accepted that use of less lead is desirable because that implies less human exposure to lead at all stages of production and use--both of the raw material itself and of the lead-containing product. It is likewise desirable to minimize human exposure by the nature of product design and the nature of manufacturing methods.
In the field of lead-acid batteries, progress has been made in recent years in reducing the handling of lead and exposure to lead in battery production. For one thing, progress has been made in recovering, recycling and reusing lead used in the manufacture of storage batteries; 96.8% is recovered according to 1991 data available from The Battery Council International. Among the advances more directly related to battery production methods are mechanization of welding operations and reduction of lead dust in manufacturing facilities.
Despite recent progress, there is a continuing need for improvements to reduce the amount of lead used in lead-acid storage batteries, to further reduce or eliminate human contact with lead in battery production and, more generally, to further reduce human exposure and health concerns related to lead use in storage batteries.
Another consideration or shortcoming with respect to lead-acid batteries has been their substantial weight or, stated differently, an energy density which is relatively low because of the heavy weight of the battery. This shortcoming is a particular concern in applications in which the power supply must be mobile, such as electric-powered vehicles, where total vehicle weight is a factor determining and limiting vehicle range.
Everyone concedes or would concede that it is wasteful and environmentally unsound to use more lead than necessary in batteries. It is also known that long electrical paths increase the internal resistance of the battery and, as a result, decrease the its energy density. Certain limited progress has been made in recent years in shortening the electrical path from the battery cells to the external battery terminals. This has been done mainly with certain "through-the-partition" cell connectors and the use of external side terminals.
Yet there is a long-standing unsatisfied need in the field of lead-acid storage batteries for batteries which have a still shorter electrical path and which, in whatever way, are substantially lower in weight and higher in energy output than the conventional lead-acid storage batteries of recent years.
Certain of the above problems and shortcomings have been addressed in earlier work, including the disclosures of my U.S. Pat. No. 3,261,719. The device of such patent has lead-receiving cavities in its base which extend from one cell to an adjacent cell and provide electrical union. The case of such device has side walls and partitions which are unitary with the top wall, and this structure is essentially glued to the base by the insertion of epoxy over the lead and most of the base in position to join with the walls and partitions.
The device of U.S. Pat. No. 3,261,719, while it does address certain problems, including the problem of potential explosions, has leakage potential because of its method of manufacture. Because of the construction of such device, heat sealing by ultrasonic welding, or other modern methods, is not easily done. Furthermore, its method of manufacture has too many steps, and is therefore potentially slow and costly. The invention was never used commercially.
Thus, the many problems noted above have remained unsolved. There is an important, long-standing need for improvement in lead-acid batteries.